Photographic process printers that utilize CRT's for exposing a photosensitive medium typically use linear deflection amplifiers to sweep the CRT electron beam across the face of the CRT. A deflection cycle normally consists of a sweep, retrace, and hold period. During the active sweep period, the CRT is unblanked and the CRT electron beam is driven horizontally at a particular vertical position while being modulated with image data to expose the medium. During the retrace period, the CRT is blanked and the CRT electron beam is returned to a home position to wait for the start of the next sweep. Thus, the sweep and retrace periods are typically fixed time intervals. The CRT electron beam is then held in the home position for the hold period until a new sweep is initiated. Therefore, the hold period may be a variable time interval dependent on the print speed. The duty cycle thus has two potential periods of off-duty time where the CRT is blanked: the retrace period and the optional hold period. These off-duty periods slow down the print process considerably.
It is thus apparent that there is a need in the art for an improved sweep method that can reduce the off-duty time in order to optimize the duty cycle and increase the print speed. There is also a need in the art to eliminate the hold period after every sweep to further optimize the duty cycle and further increase the print speed. The present invention meets these and other needs in the art.
This application is a continuation-in-part application Ser. No. 09/118,486 of Kerry L. Shaklee et al. filed on Jul. 17, 1998 entitled Bi-Directional Sweeping for Monochrome CRT Printers, which is incorporated herein by reference for all that is disclosed and taught therein.